In a steering system with rack, the steering pinion is linked in rotation with the steering column, maneuverable using the driving wheel of the vehicle, and this pinion engages with the rack slidably mounted in a steering casing of elongated shape. The two ends of the rack, external to the casing, are coupled to steering rods respectively associated with the right and left steering wheels of the vehicle. Thus, the rotation of the wheel in one direction or the other is transmitted by the steering column to the steering pinion, and is converted into a corresponding translation of the rack which, by means of the steering rods, itself causes the coordinated orientation of the two steering wheels of the vehicle, for a “sharp turning” to the right or left.
In such a steering system, the yoke device elastically acts on the back of the rack, in the region of the steering pinion, to strongly press the gearing of this rack against said pinion, thus preventing any risk of loss of contact of the gearings. The yoke device is usually exhibited as a “yoke line”, with a mobile part forming a friction pad, guided in translation and biased by elastic means towards the back of the rack.
It is also known the “eccentric” yoke devices, which replace the traditional concept of “linear” yoke by a rotating concept. In such a yoke device, it is provided a rotary pad of annular or arched shape which has an outer circular periphery and an inner periphery also circular but off centered with respect to the outer periphery thereof. The rotary pad is rotatably mounted in the steering casing, around a rotation axis parallel with the longitudinal axis of the rack. The inner off centered periphery of this pad presses against the back of the rack. The rotary pad is biased in rotation or positioned angularly in such a manner that its inner periphery, applied against the back of the rack, pushes back the latter towards the teeth of the pinion in such a manner as to keep the gearings engaged.
Particularly, French patent FR 2 951 797 or its international equivalent WO 2011/048328, on behalf of the applicant, describes a yoke device with eccentric, such as reminded above, in which a clearance compensation mechanism comprises a thrust member pressed on a radial arm of the rotary pad as a result of a compression spring inserted between the thrust member and a stationary support of the pad, or an integral element of said support. A mobile stop, rotatably mounted relatively to the support or to said element, comprises at least one gearing with stepped teeth which cooperates with at least one notch of the thrust member or vice versa. The mobile stop is linked by means of a torsion spring to the support or to the element integral with the support. Thus, the notch or notches successively cooperate with the stepped teeth of the or each gearing of the mobile stop, in such a manner as to “catch up” with the mechanical clearance in particular caused by wear.
Even more particularly, in the embodiment described by the aforementioned documents, the mobile stop is provided, at its end nearest the rotary pad, with at least two gearings with stepped teeth, disposed in as many toothed sectors, such as two diametrically opposed gearings each occupying a sector of 180°, these gearings cooperating with as many notches formed on the thrust member. The gearings of the mobile stop, by the number of two at minimum, are in theory identical, in particular to teeth all with globally triangular profile, and thus all simultaneously playing the same role.
However in practice, in the case where the mobile stop thus comprises several gearings, it may occur that due to the manufacturing defects certain toothed sectors block the rotation of the mobile stop when close to the maximum allowed clearance value, while another gearing already sees its following tooth engage on the corresponding notch of the thrust member. This may cause abnormal and premature wear of the parts of the clearance compensation mechanism and erratic operating of this mechanism, in which the contacts no longer take place on the required areas.